1. Field of the Invention
This invention relates to methods for determining the heart rate of a patient. More particularly, this invention relates to methods for rapidly determining the heart rate of a patient over a short period or window of time for immediate display to the attending physician or nurse.
2. Description of the Background Art
Presently there exist many methods or techniques for determining the heart rate of a patient. The simplest method comprises the manual averaging of heart beats over a period or "window" of time by multiplying by the number of beats by a multiplier to determine an average heart beat interval that is then used to compute the number of heart beats per minute. Longer periods or windows may be employed for more accurate heart rate determination. The longer periods necessarily result in increased response times for reporting and acting upon changing rates.
For the past decades, electronic or computerized heart rate monitors have been developed for automatically determining the average heart rate of the patient and for displaying the heart rate to the attending physician or nurse. Most of these monitors employ techniques for identifying or characterizing non-arrhythmic artifacts and activities that would otherwise skew the averaging of the heart rate. Common non-arrhythmic activities include PVCs, non-blanked pacer spikes, fast flushes, and short noisy or unstable regions.
By way of example, as shown in U.S. Pat. 4,478,224, improved heart rate determinations may be obtained by monitoring the patient's EKG signal to detect heartbeat artifacts and for producing a corresponding inhibit signal. The inhibit signal is supplied to the heart rate monitor to inhibit the heart rate determinations whenever the artifacts are detected. During operation, the heart rate monitor measures the time intervals between successive heartbeats and estimates heartbeat rate based on a plurality of such time interval measurements. If the inhibit signal ever occurs, indicating the occurrence of a heartbeat artifact, the inhibit signal inhibits the monitor from continuing to measure the current heartbeat interval.
Thereafter, when the inhibit signal terminates, indicating that the artifact is no longer present, the monitor resumes measuring time intervals after the occurrence of the next heartbeat.
As noted above, a large window results in a more accurate heart rate calculation since the number of heart beats occurring within the window is higher and the calculation is less suspectable to skewing by non-arrhythmic activities. However, the larger the window is in time, the longer the rate calculation delay. Hence, the size of the window is often critical to the time delay between rate calculations and display updates.
On the one hand, design goals often seek to minimize the window so that the heart rate may be updated and displayed in what appears as real time. On the other hand, the longer the window, the more accurate the determination of the heart rate can be, especially if the heart beats are averaged over the window.
Therefore, it is an object of this invention to provide an improvement which overcomes the aforementioned inadequacies of the prior art methods and provides an improvement which is a significant contribution to the advancement of the methods for determining heart rates.
Another object of this invention is to more accurately determine the running rate of a heart over a short period or window of time in the presence of non-arrhythmic activities such as PVCs, non-blanked pacer spikes, fast flushes, and short noisy or unstable regions.
Another object of this invention is to minimize or eliminate the non-arrhythmic activities from the calculation of the dominant heart rate during the window of time, so that the dominant heart rate calculation is not excessively skewed by the non-arrhythmic activities.
Another object of this invention is to provide a method for determining a dominant heart rate from a series of beat triggers representative of a mixed series of normal heart beats and non-arrhythmic activities.
Another object of this invention is to provide a method for determining a dominant heart rate from a series of beat triggers representative of a mixed series of normal heart beats and non-arrhythmic activities, with the beat triggers being determined at a specific sampling rate defining sample intervals, comprising the steps of framing a window to include a portion of the series of beat triggers and to be beat-aligned with a first beat trigger and a last beat trigger, the window thereby defining a plurality of trigger intervals for respective adjacent beat triggers, with each trigger interval containing a plurality of the sample intervals existing between the respective adjacent beat triggers; summing the windowed sample intervals; for each of the trigger intervals, computing a weight factor based upon the ratio of the summed windowed sample intervals to the number of sample intervals within that trigger interval; grouping the weight factors; computing the percentage of the window that each group of weight factors constitutes to determine the dominant group containing the dominant beat triggers; and analyzing the dominant beat triggers within the dominant group to determine the dominant heart rate.
The foregoing has outlined some of the pertinent objects of the invention. These objects should be construed to merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.